The need to provide an emergency path of egress lighting when normal power is lost is well known. In order to meet this need it is common practice to provide some form of battery-powered lighting in a given space. It is often convenient and desirable to provide this battery-powered auxiliary lighting within the standard or existing light fixtures. Batteries utilized in these systems are continuously charged and maintained in a full charge state. Thus, the battery charging function remains turned on and uninterrupted (i.e., unswitched) at all times.
In present practice a fluorescent ballast or a light-emitting diode (LED) driver provides for the normal operation of the fixture's light source and this device may be switched on and off. A separate battery backup unit then provides the functions of battery charging, input line voltage detection, power conversion, load transfer switching and test operations. This unit, since it contains the battery charging function, remains on at all times and is unswitched.
In the lighting industry, input line voltages typically range from 120 volts to 277 volts AC, operating at a frequency of 60 Hz. The input line voltage is often called line voltage, mains, main power supply, or main input supply. In some cases, other frequencies and even higher voltages are utilized, such as 347 volts and 480 volts. Thus the ballast or driver, as well as the battery backup module, should be capable of accepting at least these voltage levels through line interface circuitry. It will be understood that this interface to the power main is critical, and the associated circuitry will be the most vulnerable to external phenomenon (e.g., power surges, lightning strikes, equipment failures, fluctuations in power, etc). In present practice, there is duplication of the line interface function, since it is present in both the ballast or driver and the battery backup module. The line interface function is not trivial, and it requires high power factor, transient protection, electromagnetic interference (EMI) suppression, as well as start-up accommodations and many other features.
Thus, to reduce cost and the possibility of failure, it is desirable to reduce the quantity of line interface circuits, while maintaining the full functionality of the battery charging functions and ballast or driver during both normal operation and emergency operation. It is also desirable to increase communication between the ballast or driver and the battery backup module, to improve both normal and emergency operation of the lighting system.